Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art ignite an air/fuel mixture to produce heat. In one example, fuel injected into a combustion chamber of the engine is ignited by way of a spark plug, a glow plug, or an AC/DC ignition source. The heat and expanding gases resulting from this combustion process are directed to displace a piston or move a turbine blade, both of which can be connected to a crankshaft of the engine. As the piston is displaced or the turbine blade is moved, the crankshaft is caused to rotate. This rotation is utilized to directly drive a device such as a transmission to propel a vehicle, or a generator to produce electrical power.
During operation of the engine described above, a complex mixture of air pollutants can be produced as a by product of the combustion process. These air pollutants are composed of, among other things, the oxides of nitrogen (NOX). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOX emitted to the atmosphere from an engine is regulated depending on the type of engine, size of engine, and/or class of engine.
It has been established that a well-distributed combustion flame having a low flame temperature can reduce NOX production to levels compliant with current emission regulations. One way to generate a well-distributed flame with a low flame temperature is to introduce a lean air/fuel mixture into the combustion chambers of the engine. This lean mixture, when ignited, burns at a relatively low temperature. The lowered combustion temperature slows the chemical reaction of the combustion process, thereby decreasing the formation of NOX. As emission regulations become stricter, leaner and leaner mixtures are being implemented.
Although successful at reducing emissions, very lean air/fuel mixtures are difficult to ignite. That is, a conventional igniter (spark plug, glow plug, etc.) may be insufficient to initiate and/or maintain combustion of a mixture that has little fuel (compared to the amount of air present). As a result, the emission reduction available from a typical engine operated in a lean mode may be limited. In addition, conventional igniters suffer from low component life.
One attempt at improving combustion initiation of a lean air/fuel mixture is disclosed in U.S. Pat. No. 7,171,924 (the '924 patent), issued to Robel et al. on Feb. 6, 2007. The '924 patent discloses an internal combustion engine having a combustion chamber, and a piston slidably disposed within the combustion chamber. The piston is configured to reciprocate through a compression stroke to pressurize an air/fuel mixture within the combustion chamber. The internal combustion engine also has an air supply and a fuel supply in selective fluid communication with the combustion chamber. The internal combustion engine further has a supply of non-combustible gas, and an injector in fluid communication with the combustion chamber and the supply of non-combustible gas. The injector is configured to inject the non-combustible gas from the supply into the combustion chamber at a time during or just after completion of the compression stroke to cause auto-ignition of the pressurized air/fuel mixture within the combustion chamber. In one example, the non-combustible gas includes recirculated exhaust. In this manner, ignition of a lean air/fuel mixture may be possible without the use of a conventional igniter.
Although the engine of the '924 patent benefits from auto-ignition of a lean air/fuel mixture, improvements may still be possible. Specifically, in some situations such as during startup or cold operation, the injection of non-combustible gas may, alone, be insufficient to promote auto-ignition.
The disclosed ignition control system is directed to overcoming one or more of the problems set forth above.